CURLOPT_SSLVERSION

Section: curl_easy_setopt options (3)
Updated: November 04, 2020
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NAME

CURLOPT_SSLVERSION - set preferred TLS/SSL version

SYNOPSIS

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSLVERSION, long version);

DESCRIPTION

Pass a long as parameter to control which version range of SSL/TLS versions to use.

The SSL and TLS versions have typically developed from the most insecure version to be more and more secure in this order through history: SSL v2, SSLv3, TLS v1.0, TLS v1.1, TLS v1.2 and the most recent TLS v1.3.

Use one of the available defines for this purpose. The available options are:

CURL_SSLVERSION_DEFAULT: The default acceptable version range. The minimum acceptable version is by default TLS v1.0 since 7.39.0 (unless the TLS library has a stricter rule).
CURL_SSLVERSION_TLSv1: TLS v1.0 or later
CURL_SSLVERSION_SSLv2: SSL v2 (but not SSLv3)
CURL_SSLVERSION_SSLv3: SSL v3 (but not SSLv2)
CURL_SSLVERSION_TLSv1_0: TLS v1.0 or later (Added in 7.34.0)
CURL_SSLVERSION_TLSv1_1: TLS v1.1 or later (Added in 7.34.0)
CURL_SSLVERSION_TLSv1_2: TLS v1.2 or later (Added in 7.34.0)
CURL_SSLVERSION_TLSv1_3: TLS v1.3 or later (Added in 7.52.0)

The maximum TLS version can be set by using one of the CURL_SSLVERSION_MAX_ macros below. It is also possible to OR one of the CURL_SSLVERSION_ macros with one of the CURL_SSLVERSION_MAX_ macros. The MAX macros are not supported for WolfSSL.

CURL_SSLVERSION_MAX_DEFAULT: The flag defines the maximum supported TLS version by libcurl, or the default value from the SSL library is used. libcurl will use a sensible default maximum, which was TLS v1.2 up to before 7.61.0 and is TLS v1.3 since then - assuming the TLS library support it. (Added in 7.54.0)
CURL_SSLVERSION_MAX_TLSv1_0: The flag defines maximum supported TLS version as TLS v1.0. (Added in 7.54.0)
CURL_SSLVERSION_MAX_TLSv1_1: The flag defines maximum supported TLS version as TLS v1.1. (Added in 7.54.0)
CURL_SSLVERSION_MAX_TLSv1_2: The flag defines maximum supported TLS version as TLS v1.2. (Added in 7.54.0)
CURL_SSLVERSION_MAX_TLSv1_3: The flag defines maximum supported TLS version as TLS v1.3. (Added in 7.54.0)

In versions of curl prior to 7.54 the CURL_SSLVERSION_TLS options were documented to allow only the specified TLS version, but behavior was inconsistent depending on the TLS library.

DEFAULT

CURL_SSLVERSION_DEFAULT

PROTOCOLS

All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.

EXAMPLE

CURL *curl = curl_easy_init();
if(curl) {
  curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

  /* ask libcurl to use TLS version 1.0 or later */
  curl_easy_setopt(curl, CURLOPT_SSLVERSION, CURL_SSLVERSION_TLSv1);

  /* Perform the request */
  curl_easy_perform(curl);
}

AVAILABILITY

SSLv2 is disabled by default since 7.18.1. Other SSL versions availability may vary depending on which backend libcurl has been built to use.

SSLv3 is disabled by default since 7.39.0.

RETURN VALUE

Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.